if you want to, you can use the standard icons for Gold, Silver and Copper by simply doing the following:
local COPPER_ICON = "|TInterface\\MONEYFRAME\\UI-CopperIcon:0:0:0:-1|t"
local SILVER_ICON = "|TInterface\\MONEYFRAME\\UI-SilverIcon:0:0:0:-1|t"
local GOLD_ICON = "|TInterface\\MONEYFRAME\\UI-GoldIcon:0:0:0:-1|t"
COPPER_A...